1. Field
The present disclosure relates to a complex for an anode active material, an anode including the complex, a lithium secondary battery including the anode, and methods of preparing the complex.
2. Description of the Related Art
Silicon-based anode materials with high capacity (theoretically about 4,200 mAh/g) have drawn attention as anode materials of next generation lithium batteries. However, the volume of the silicon-based anode materials expands 300% or greater during intercalation and deintercalation of lithium. Such a large volume expansion may cause cracks and pulverization of the silicon-based anode material, resulting in electrical short circuits and continuous decomposition of an electrolyte. Accordingly, charge/discharge characteristics (e.g., initial charge/discharge efficiency, average charge/discharge efficiency, lifespan characteristics, and high-rate discharge characteristics) of the anode material rapidly deteriorate, and thus commercialization of a silicon-based anode material has been delayed despite its high theoretical capacity.
In order to improve these characteristics, much research has been conducted into developing an anode material with high capacity and excellent charge/discharge characteristics by changing the shape and structure of silicon. Although research has recently been conducted into preventing deterioration of battery characteristics due to volume expansion of silicon-based anode materials by introducing porous silicon particles and controlling nanostructures such as silicon nanowires and nanotubes, such nanostructure control technology uses expensive processing techniques such as high-temperature vacuum chemical vapor deposition, sacrificial templating, and chemical etching. Thus, it is difficult to commercialize the silicon-based anode materials. In addition, nano-sized particles have a large specific surface area which can contribute to adverse thermal stability of batteries, further impeding commercialization.
For example, a method of preparing three-dimensional porous silicon by depositing a plurality of silver particles on bulk silicon and forming a plurality of pores in the bulk silicon by chemical etching has been attempted. In the method, the plurality of pores reduces a total expansion ratio of the silicon. However, this method uses an expensive noble metal and the porous silicon has relatively low porosity.
As another example, a method of preparing double-walled silicon nanotubes (DWSINTs) by forming a coating layer on external walls of silicon nanotubes using a carbonaceous material has been attempted. According to this method, the expansion ratio of silicon may be reduced by the coating layer. However, commercialization thereof is difficult because it uses specialized methods, such as chemical vapor deposition (CVD).
Therefore, there is a need to develop an anode active material having a high capacity and improved charge/discharge characteristics, e.g., initial discharge capacity, initial charge/discharge efficiency, and lifespan characteristics.